Ryanair is facing another probe from the Office of Fair Trading, into how it sells fares to the public. The Advertising Standards Authority has made a formal complaint.

A long-running spat between the British advertising regulator and Europe's largest budget airline came to a head when the ASA referred Ryanair to the government's consumer watchdog. Ryanair also made a referral today, but the ASA confirmed that it had contacted the OFT first.

In a letter to Ryanair's head of mark­eting, Dara Brady, the regulator said it had lost patience with the airline after a slew of negative rulings. It said repeated refusals to confirm the number of flights available in a £10-seat offer advertised in national newspapers last year left it no choice but to make a referral.

"Because of Ryanair's unwillingness and apparent inability to comply with the code rules on misleadingness over the past two years, we referred them to the OFT for the OFT to consider taking appropriate action against Ryanair using the powers available to them," said the ASA.

Ryanair was forced to close its website in February after the OFT ordered it to remove misleading prices. The closure cost an estimated £20m in lost sales, accor­ding to analysts, after technical glitches resulted in a longer-than-expected blackout.

Ryanair said it submitted a complaint to the OFT about the "Absolutely Stupid Asses" watchdog and denied that descri­bing the ASA as illiterate and innumerate had reduced its chances of a workable relationship. A spokesman said: "Ryanair is not going to sit there and take rulings from the ASA that are completely false."

However, it has benefited from positive ASA rulings recently, including one last month that found in favour of Ryanair against easyJet. An easyJet spokesman said on Friday: "It's similar to agreeing to play a game of football but not liking it when the referee rules against them."